The present invention involves aerosol production of finely-divided particles of a variety of compositions. The present invention also involves the particles so manufactured and electronic devices made using the particles.
Powdered materials are used in many manufacturing processes. One large use for powders is for thick film deposition to prepare films of a variety of materials. Some thick film applications include, for example, deposition of phosphor materials for flat panel displays, and patterning of eclectically conductive features for electronic products.
For thick film applications, and for other applications, there is a trend to use powders of ever smaller particles. Generally desirable features in small particles include a small particle size; a narrow particle size distribution; a dense, spherical particle morphology; and a crystalline grain structure. Existing technologies for preparing powdered products, however, often could be improved with respect to attaining all, or substantially all, of these desired features for particles used in thick film applications.
One method that has been used to make small particles is to precipitate the particles from a liquid medium. Such liquid precipitation techniques are often difficult to control to produce particles with the desired characteristics. Also, particles prepared by liquid precipitation routes often are contaminated with significant quantities of surfactants or other organic materials used during the liquid phase processing.
Aerosol methods have also been used to make a variety of small particles. One aerosol method for making small particles is spray pyrolysis, in which an aerosol spray is generated and then converted in a reactor to the desired particles. Spray pyrolysis systems have, however, been mostly experimental, and unsuitable for commercial particle production. Furthermore, control of particle size distribution is a concern with spray pyrolysis. Also, spray pyrolysis systems are often inefficient in the use of carrier gases that suspend and carry liquid droplets of the aerosol. This inefficiency is a major consideration for commercial applications of spray pyrolysis systems.
There is a significant need for improved manufacture techniques for making powders of small particles for use in thick film and other applications.
Not only would improved particle manufacture techniques be desirable, but improved materials would also be desirable for a variety of applications. For example, there is a significant problem in cofire processes, such as cofiring of multi-layer ceramic capacitors and other components, of delaminations and other failures that can occur due to sintering/densification/shrinkage mismatch between adjoining layers. Improved techniques for providing high quality particles to reduce these problems would be desirable.
The present invention provides an aerosol process for manufacturing finely-divided powders of a variety of materials having desirable properties and at commercially acceptable rates. Apparatus is also provided for implementing the manufacturing method.
An important aspect of the present invention is aerosol generation. An aerosol generator and aerosol generation method are provided that are capable of producing large quantities of a high quality, dense aerosol for spray pyrolysis operations. This is significantly different from aerosol generation that has previously occurred with respect to spray pyrolysis particle manufacture in small-scale, laboratory systems. An aerosol generator is provided including an array of ultrasonic transducers underlying a single reservoir of precursor solution that is ultrasonically energized to produce the aerosol. Careful distribution of carrier gas to different portions of the reservoir results in an efficient use of carrier gas in making a dense aerosol and at a high rate suitable for commercial applications.
The process is versatile for preparing powders of a number of materials. An important group of powders prepared with the process of the present invention include multi-phase particles.
Particularly advantageous are multi-phase particles designed for use in manufacturing electrically-conductive metallic films for electronic products. The multi-phase particles include a metallic phase and a non-metallic phase. In one preferred type of multi-phase particles, the non-metallic phase comprises at least one of silica, alumina, titania and zirconia. In another preferred type of multi-phase particles, the non-metallic phase includes a titanate, such as barium titanate, neodymium titanate or other titanates as discussed below.
Yet another important type of multi-phase particles of the present invention include those having a metallic phase and a non-metallic phase including elemental carbon. These multi-phase particles are useful as electrode materials and as catalysts.
The present invention also provides electronic products including a dielectric layer adjoining an electrically conductive film that has been formed using multi-phase particles of the present invention, and especially using multi-phase particles including a titanate as the non-metallic phase. In this way, the electrically conductive film may be cofired with a titanate dielectric layer with improved compatibility between the layers, for reduced delaminations and other failures.
These and other aspects of the invention are discussed in more detail below.